Shale oil recovery from fractured oil shale

ABSTRACT

Shale oil is recovered from vertically fractured oil shale formations by injecting hot solvent into the bottom of the fractured zone, removing shale oil from a point above the point of injection, then incrementally raising the recovery point to maintain the recovery point above the level of the silt sedimented within the fracture chimney.

[451 May 1, 1973 United States Patent 1 Allred 8/1969 Parker.......,................,......

y fractured oil nt into the botthen incrementally raising the recovery point to maintain the recovery point above the level of the silt sedimented within the fracture chimney.

Primary Examiner-Robert L. Wolfe Att0rney.loseph C. Herring, Richard C. Willson, Jr. and Jack L. Hummel [57] ABSTRACT Shale oil is recovered from verticall shale formations by injecting hot solve tom of the fractured zone, removing shale oil from a point above the point of injection,

9 Claims, 3 Drawing Figures ,...166/247 X Closmann.........................166/247 X Mar. 23, 1971 Appl. No.: 127,266

Field of Search...........

References Cited UNlTED STATES PATENTS 6/1970 10/1967 Sch1icht.........

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SHALE DESCRIPTION OF THE PRIOR ART shale; U.S. Pat. No. 3,358,756 which percolates o benzene in a manner similar to that of the aforementioned U.S. Pat. No. 1,422,204; U.S. Pat. No. 3,515,213 which recovers shale oil by circulating a fluid heated at a moderate temperature from one point within the formation to another for a relatively long time until some of the organic components contained in the shale oil formation are converted to oil-shalederived fluidizable materials; U.S. Pat. No. 3,528,501 producesshale oil in situ by injecting hot hydrocarbon oil through a fractured section of shalebetween wells penetrating the oil shale formation; U.S. Pat. No. 3,241,611 which recovers petroleum from oil shale by circulating natural gas at elevated temperature and pressure as a solvent for the kerogen. None of the above patents teach the incremental raising of the injection and withdrawal points to accomplish the advantages of the present invention.

SUMMARY OF THE INVENTION General Statement of the Invention According to the present invention, shale oil is recovered by first causing a vertical fracture in an oil shale formation, e.g., by explosion, preferably an underground nuclear explosion.

See, for example, Education for Peaceful Uses of 1 Nuclear Explosives, Lynn E. Weaver, ed. The University of Arizona Press, Tucson, Ariz. (1970) (pp 45-63) and The Constructive Uses of Nuclear Explosives, Edward Teller, Wilson Talley, Gary Higgins, Gerald W.

Johnson, McGraw Hill, NYC NY (1968) (pp 245-265) LC No. 6811621.

The device, or devices, will generally be placed near the bottom of the oil shale formation, or if multiple devices, at predetermined intervals, and exploded causing a fracture chimney" which will reach to the top of oil shale formation. Within this chimney will be rubble composed of a wide size range of oil shale resulting from the fracturing by the explosion and the subsequent collapse into the nuclear formed cavity.

A string of pipe is inserted into the chimney by conventional drilling techniques which drill through the rubble. The pipe should extend to a point very near the bottom of the chimney. A second pipe should also be inserted and extend downward to a point somewhat higher than the bottom of the first pipe. The two pipes can be concentric, if desirable, to avoid the need for drilling a second hole through the rubble in the chimney.

To initiate the process, a hot solvent, e.g., stabilized (Material that will not polymerize on prolonged heating, obtained, e.g., by conventional coking or hydrotreating'.) shale oil, kerosine or coker gas oil is heated to about 800F. and injected through the first pipe (the injection pipe) into the bottom of the chimney. The hot solvent contacts oil shale in the rubble and in the walls of the chimney extracting shale oil by breaking down the kerogen within the oil shale and 2 leaving a by product, silt, composed primarily of clays, sand and dolemitic carbonates which is insoluble in the solvent. The mixture of shale oil plus solvent is then withdrawn through the second pipe (the withdrawal pipe). The withdrawn mixture is settled to remove any entrained silt and is fractionated (hydrogenated if required) to remove a fraction boiling above about 750, more preferably 800, and most preferably 850. The lower fraction is then heated and reinjected into the chimney. Through losses by evaporation, etc. the solvent will gradually become virtually percent composed of the stabilized fraction from the shale oil.

One of the characteristics of many oil shales, e.g.,

Green River Oil shales (i.e. greater than 20 gal/ton) is Circulation of ,the hot solvent continues until the level of silt rises to the point where it either affects the flow of hot solvent into the chimney or begins to be elutriated out through the withdrawaltube causing excessive need for above-surface settling. At this point, the withdrawal tube and the injection tube are both raised so that they are above the level of the silt in the chimney. The process then repeats with the lower end of the withdrawal tube generally being slightly above the lower end of the injection tube and with both tubes being raised so as to keep them above the level of the silt which gradually buildsup in the chimney.

Utility of the Invention Shale oil is, of course, useful for the wide variety of purposes to which hydrocarbons are commonly put, including the production of gasoline, diesel fuel, jet fuel, fuel oil, lubricants, solvents, starting materials for plastics, feed for pyrolysis processes, etc. all as well described in the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic drawing of a chimney within an oil shale formation and the equipment used to heat, fractio'nate and circulate the hot solvent for recovery of the shale oil.

FIG. 2 shows schematically the chimney of FIG; I after recovery of the oil shale is: well under way and showing how the injection and withdrawal tubes have been raised as the, level of silt rises in the chimney.

FIG. 3 is a detail of the lower end of preferred concentric injection and withdrawal tubes.

DESCRIPTION or THE PREFERRED EMBODIMENTS Starting Materials The solvents used with the present invention are, ini" tially, any convenient commercial solvent which will extract shale oil from the kerogen in the oil shale. For example, coker gas oils, kerosine, catalytic cycle oils, stabilized crude oil, or shale oil derived from another subterranean formation can be injected .in order to initiate the process.

See, for example: USBM Bul 533, Thermal Solution and Hydrogenation of Green River Oil Shale. H.B.Jensen, W.I.Barnet, & W.I.R.Murphy, U.S.Govt. Printing Office (1953).

Once the process is initiated, the preferred solvent will be, at least in part, a fraction derived from the oil shale itself so that the process becomes self-sustaining as to the solvent. Preferred fractions are those discussed above under Summary of the Invention.

Of course, other solvents or mixtures of them can be added to the fraction of the shale oil which is circulated through the chimney or shale oil itself can be circulated through the'chimney without fractionation, if desired.

In addition to electricity required for operating the circulating pumps and other apparatus, the only other material needed for use with the present invention is a fuel e.g., natural gas, crude oil, residual oil, coal, or shale oil itself to be used for firing the heater which heats the solvent prior to its recirculation through the chimney.

Temperature: Though not narrowly critical, the temperature of the solvent when it contacts the oil shale should be in the general range of preferably from 750F. to about 950F., more preferably from 800F. to about 900F., and most preferably from 825 to about 850.

Pressure: Although the entire operation can be conducted at substantially hydrostatic pressure, it may, in some instances, be desirable to somewhat pressurize the chimney in order to maintain more intimate contact between the solvent and the oil shale being extracted. The depth of the overburden will determine the maximum pressure which can be employed.

Time: The contact time between the solvent and the oil shale is not narrowly critical and may readily be adjusted for optimum results. The volume of solvent in the chimney at any given time will be adjusted accordingly.

Batch or Continuous Basis: While the examples, and most of the application, of the present invention will utilize the process on a continuous basis, the process can be employed on a batch basis where desirable. For example, the same tube may serve as both the injection tube and the withdrawal tube so that a quantity of solvent is first injected, then allowed to contact the oil shale for a sufficient time, and then withdrawn. Example: Referring to FIG. 1, a cavity has been created by a nuclear blast and is filled with rubble 11. Hot solvent, in this case hot coker gas oil, has been pumped downward through injection pipe 12 forming a pool 13 on top of fine silt-like material 14 at the bottom of the cavity. Solvent plus shale oil is withdrawn through eduction tube 15 located on the other side of the cavity from injection tube 12. Both tubes have means for gradually raising the level at which they communicate with the cavity. A pump 16 located downhole causes the withdrawal of solvent. The withdrawn solvent moves through a settling tank 17 into a fractionator 18 from which a fraction 19 is withdrawn for processing in a conventional refinery. The remaining fraction boiling above about 750F. is sent to heater 20 which heats it to a temperature of approximately 850F. A pump 21 then injects this hot solvent fraction back into the cavity.

FIG. 2 shows the identical cavity after the silt layer has risen much higher to effect extraction of a much larger amount of the oil shale rubble. Note that both tubes have now been raised to remain in the solvent layer but above the level of the silt. This process is continued until the silt level reaches the top of the cavity after which the apparatus is withdrawn and may be moved to another site.

FIG. 3 shows a modification of the invention in which the injection tube 30 and the withdrawal tube 31 are concentric with each other. The apparatus is otherwise similar to that shown in FIGS 1 and 2.

Modifications of the Invention It should be understood that the invention is capable of a variety of modifications and variations which will be made apparent to those skilled in the art by a reading of the specification and which are to be included within the spirit of the claims appended hereto. For example, various pumping devices, distillation apparatus, and heaters may be employed. The distillation apparatus may itself be eliminated and the process practiced, using only a recycle of a portion of the oil shale produced. The various techniques of the prior art are adaptable to the invention. For example, wells can be drilled into a portion of the overburden and fractured either hydraulically or explosively to cause additional quantities of overburden to fall into the original retort.

Also, in some cases, the solvent may be injected at or near the top of the cavity to avoid raising the injection point and to provide maximum solvent-oil shale contact.

What is claimed is:

1. In process for the recovery of shale oil from formations comprising oil shale, the improvement comprising in combination, forming within said formation a vertically fractured chamber by explosive means, injecting hot solvent through an injection point into the bottom of said vertically fractured chamber, to extract shale oil, removing the shale oil and solvent from a recovery point located above the bottom of said vertically fractured chamber, allowing the residual silt to settle within said vertically fractured chamber, and thereafter incrementally raising the recovery point to maintain the recovery point above the level of silt sedimented within said chamber. I

2. The process of claim 1 wherein the hot solvent is stabilized shale oil or a fraction thereof.

3. A process according to claim 1 wherein the hot solvent has a temperature from about 750 to about 950F when it contacts said oil shale.

4. A process according to claim 1 wherein said hot solvent is injected through an injection pipe extending downward into the fractured zone and said shale oil and solvent and removed through a recovery pipe extending from said recovery point to the surface.

5. A process according to claim 4 wherein said injection pipe and said recovery pipe are concentric with each other.

6. A process according to claim 1 wherein said fractured zone is formed by an underground nuclear explosion.

7. A process according to claim 1 wherein said oilshale comprises Green River oil shale.

8. A process according to claim 4 wherein said fractured zone is formed by an underground nuclear explosion and wherein said solvent comprises shale oil and said solvent has a temperature of from about 800 to about 900F. when it contacts said oil shale. 

2. The process of claim 1 wherein the hot solvent is stabilized shale oil or a fraction thereof.
 3. A process according to claim 1 wherein the hot solvent has a temperature from about 750 to about 950* F when it contacts said oil shale.
 4. A process according to claim 1 wherein said hot solvent is injected through an injection pipe extending downward into the fractured zone and said shale oil and solvent and removed through a recovery pipe extending from said recovery point to the surface.
 5. A process according to claim 4 wherein said injection pipe and said recovery pipe are concentric with each other.
 6. A process according to claim 1 wherein said fractured zone is formed by an underground nuclear explosion.
 7. A process according to claim 1 wherein said oil shale comprises Green River oil shale.
 8. A process according to claim 4 wherein said fractured zone is formed by an underground nuclear explosion and wherein said solvent comprises shale oil and said solvent has a temperature of from about 800* to about 900*F. when it contacts said oil shale.
 9. A process according to claim 1 wherein the injection point is located near the top of the fractured zone so that the injected solvent runs down over the fractured oil shale toward the bottom of the zone. 